A cylindrical rod having temperature `T_1` and `T_2` at its end. The rate of flow of heat `Q_1` cal/sec. If all the linear dimension are doubled keeping temperature remain const. then rate of flow of heat `Q_2` will be : -

Options

A. `4Q_(1)`
B. `2Q_(1)`
C. `Q_(1)//4`
D. `Q_(1)//2`

Answer

B

Explanation

`Q_(1) prop r^(2)//l, Q_(2) prop 4r^(2)//2l = 2r^(2)//l`
`Q_(2)//Q_(1) = 2, Q_(2) = 2Q_(1)`